Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$6.79	11.379%	$7.5626	$7.56	$7.55	$7.60
Purchase #2	$42.72	13.700%	$48.5726	$48.57	$48.55	$48.60
Purchase #3	$13.39	10.111%	$14.7439	$14.74	$14.75	$14.70
Purchase #4	$188.28	4.354%	$196.4777	$196.48	$196.50	$196.50
Purchase #5	$119.59	10.763%	$132.4615	$132.46	$132.45	$132.50
Purchase #6	$51.62	4.617%	$54.0033	$54.00	$54.00	$54.00
Purchase #7	$41.44	6.477%	$44.1241	$44.12	$44.10	$44.10
7 purchase totals =	$463.83		$497.9457	$497.93	$497.90	$498.00